The present invention relates to an optical information recording and reproducing system using a semiconductor laser as a light source for recording and/or reproducing information on the information recording medium.
There have been used, as a semiconductor laser source with less noises inherent to the optical feedback, a semiconductor laser with the superimposition of a high-frequency current of 500-1000 MHz and a semiconductor laser (a laser diode with independent pulsating emission) which operates at 1 GHz or higher on a direct current basis. In order to further reduce noises inherent to the optical feedback, the overall system using the semiconductor laser must be constructed suitably. It is known that a system using a semiconductor laser with the superimposition of a high-frequency current has its noise level increasing or decreasing depending on the high-frequency current superimposed and the arrangement of the optical system (JP-A-59-210541, JP-A-60-101735). In contrast, it is not yet clear how to construct the system suitably for reducing the optical feedback noise in the case of the laser diode with independent pulsating emission.